Tunable LC filter

Abstract

An inductor-capacitor (LC) filter designed to comply with EMC (Electromagnetic Compatibility) standards comprises capacitors; switches for coupling capacitors; differential-mode inductors for coupling capacitors and switches; and common-mode inductors or a combination of differential-mode inductors and common-mode inductors, where an input signal changes the inductance of differential-mode inductors in the LC filter to modify a frequency response of the LC filter. In the LC filter, differential-mode inductors further comprise identical multiple-winding inductors, and the input signal, which biases the plurality of differential-mode inductors, includes a DC signal or a combination of DC and AC signals. A corner-frequency of the LC filter is adjusted and approximated as: fc=1/(2×pi×sqrt(L×C)), where fc is the corner-frequency, L is a composite value of inductance, and C is a composite value of capacitance.

What is claimed is: 
     
       1. An inductor-capacitor (LC) filter comprising:
 a plurality of capacitors; 
 a plurality of switches for coupling the plurality of capacitors directly; one or more of the plurality of switches are connected in series with one or more of the plurality of capacitors; 
 a plurality of differential-mode inductors for coupling the plurality of capacitors and the plurality of switches directly, 
 wherein an input signal changes an inductance of the plurality of differential-mode inductors in the LC filter to modify a frequency response of the LC filter, 
 wherein the input signal includes a DC (direct current) signal or a combination of DC and AC (alternating current) signals, 
 wherein the LC filter is tuned by the input signal, and a corner-frequency of the LC filter is adjusted to multiple values, where each value imitates a corresponding fixed-corner-frequency filter in the LC filter, and 
 wherein the LC filter is designed to comply with EMC (Electromagnetic Compatibility) standards and reduces and spreads EMC spectral peaks by transferring energy of the EMC spectral peaks to sidebands of the LC filter. 
 
     
     
       2. The LC filter according to  claim 1 , wherein the plurality of differential-mode inductors comprises a plurality of identical multiple-winding inductors. 
     
     
       3. The LC filter according to  claim 1 , wherein the corner-frequency of the LC filter is adjusted and approximated as:
     fc= 1/(2×pi×sqrt( L×C )),
 
 wherein fc is the corner-frequency of the LC filter; 
 L is a composite value of inductance of the LC filter; and 
 C is a composite value of capacitance of the LC filter. 
 
     
     
       4. The LC filter according to  claim 1 , wherein the input signal biases the plurality of differential-mode inductors. 
     
     
       5. The LC filter according to  claim 1 , wherein the plurality of differential-mode inductors further function as a plurality of common-mode inductors. 
     
     
       6. An inductor-capacitor (LC) filter comprising:
 a plurality of capacitors; 
 a plurality of switches for coupling the plurality of capacitors directly; one or more of the plurality of switches are connected in series with one or more of the plurality of capacitors; 
 a plurality of common-mode inductors for coupling the plurality of capacitors and the plurality of switches directly, 
 wherein an input signal changes an inductance of the plurality of common-mode inductors in the LC filter to modify a frequency response of the LC filter, 
 wherein the input signal includes a DC (direct current) signal or a combination of DC and AC (alternating current) signals, 
 wherein the LC filter is tuned by the input signal, and a corner-frequency of the LC filter is adjusted to multiple values, where each value imitates a corresponding fixed-corner-frequency filter in the LC filter, and 
 wherein the LC filter is designed to comply with EMC (Electromagnetic Compatibility) standards and reduces and spreads EMC spectral peaks by transferring energy of the EMC spectral peaks to sidebands of the LC filter. 
 
     
     
       7. The LC filter according to  claim 6 , wherein the corner-frequency of the LC filter is adjusted and approximated as:
     fc= 1/(2×pi×sqrt( L×C )),
 
 wherein fc is the corner-frequency of the LC filter; 
 L is a composite value of inductance of the LC filter; and 
 C is a composite value of capacitance of the LC filter. 
 
     
     
       8. The LC filter according to  claim 6 , wherein the plurality of common-mode inductors further function as a plurality of differential-mode inductors. 
     
     
       9. The LC filter according to  claim 6 , wherein the plurality of common-mode inductors comprise a 2-winding common-mode inductor or a 3-winding common-mode inductor,
 wherein the 2-winding common-mode inductor has 2 coils and the 3-winding common-mode inductor has 3 coils. 
 
     
     
       10. The LC filter according to  claim 6 , wherein the input signal biases the plurality of common-mode inductors.